Method and means for detecting flaws



Feb. 6, 1934. H. c. DRAKE ET AL 1,946,196

METHOD AND MEANS FOR DETECTING FLAWS Filed March 18, 1955 3mm orsHarcourt C.Dmke t Loren J. Delaniy Patented Feb. 6, 1934 PATIENT OFFICEUNITED STATES Harcourt C. Drake,

Lanty, Spring Valley, Products, Inc., Broo of New York Hempstead, andLoren J. De

N. Y., klyn, 'N-

assignors to Sperry a corporation Application March 18, 1933. Serial No.661,484 10 Claims. (01.175-183) This invention relates to a method ofand means for detecting internal fissures in electrical conductors andmagnetizable objects. The invention has application to the generalmethod of testing which consists in energizing a conductor with fiuxeither by passing current therethrough or by magnetizing the objectunder test by means of an electromagnet. While the object under test isuniform there is uniformity in the flux but when a region of flaw isencountered the flux is distorted and such distortion is detected bysuitable detecting means.

It is one of the prinicipal objects of our invention to provide a newmethod of detecting fissures in electrical conductors and magnetizableobjects which will perform the important function of differentiatinginternal fissures from mere surface defects. Surface defectssuch asburns on rail surfaces are not the type of defect which it is thefunction of these devices to discover,-since such surface defects arenot defects in the internal structure of the conductor or magnetizableobject and the principal purpose of these detecting devices is to detectinternal defects.

By our invention we supply a means whereby it is possible readily todifferentiate between surface defects and internal fissures.

Further objects and advantages of this invention will become apparent inthe following detailed description.

In the accompanying drawing,

Fig. 1 is a side elevation of a portion of a car adapted to travel alongrails and having our invention applied thereto.

Fig. 2 is a diagrammatic representation of the principle underlying ourinvention.

Fig. 3 is a modified form of the invention disclosed in Figs. 1 and 2.

Referring first to Fig. 2, there is illustrated a method which is nowextensively employed in the testing of electrical conductors such as arail R. In this form, current is supplied to the rail from a generator Gby means of brushes 10 and 11 in engagement with the conductor toestablish an electromagnetic field surrounding the conductor. Detectormeans such as a pair of opposed coils 12, 13, maintained in constantrelation to the conductor surface is moved therealong to cut the linesof force surrounding the conductor. When a region of flaw is encounteredone coil enters said region beforethe other and thus there is induced adifferential E. M. F. between said coils which may be suitablyindicated, as, for instance, by a recording pen P operating on a chartC, said pen forming the armature of a relay M which may be energized bysaid differential induced E. M. F. by way of a suitable amplifier. Thedifficulty arising in the use of this method has been the elimination ofsurface defects which, as hereinbefore explained, are not the defectswhich it is desired to detect. Various methods have been worked out forreducing, the number of such surface defects which are picked up, one ofthese methods being that shown in Fig. 1 wherein a small detectorcarriage 20 is mounted on a current brush carriage 21 which supports thecurrent brushes 10 and 11, said detector carriage 20 being so mounted onthe current brush carriage 21 as to permit movement independent of thecurrent brush carriage and thus the detector carriage may align itselfwith the irregularities in the surface to maintain the coils 12, 13 atall times a constant distance above the rail even when passing oversurface defects.

By this invention we provide another method for segregating indicationsdue to internal defects from those due to surface defects. For thispurpose we propose the following method and apparatus:

It is well known that while direct current tends to pass into the centerof a conductor, alternating current tends to cling to the surface andthere is obtained a very marked skin effect, that is, the current clingsto the periphery of the conductor. If therefore, alternating current ofa predetermined frequency is supplied to a conductor R from agenerator Gby way of brushes 10', 11 said current will cling to the surface of theconductor and will not be affected by internal defects but only bysurface defects, so that only the latter will cause distortion of theelectromagnetic field surrounding the conductor, and hence thedifferential -E. M. F. which is picked up by a pair of opposed coils 12,13' supported on a carriage 20' will indicate only a surface defect.Said differential E. M. F. may be caused to operate a pen P similar topen P actuated by relay or energized from the output of an amplifierwhich suitably amplifies the differential E. M. F. induced by coils 12',13. The carriage 20' may be supported on the same current brush carriage21 which supports carriage 20, said carriages 20 and 20' being spacedfrom one another, or carriage 20' may be supported on a separate currentbrush carriage 21.

We cause the pen P to make a record on the same chart C parallel to therecord made by pen P. We now have the following situation-coils 12 and13 will .induce a differential E. M. F. when a defect is present whethersaid defect is due to is a surface defect. If, therefore, as indicated3. on the chart, both pens give an indication at conductors, and fordliferentiatmg between inthe same point it means that the indication isdue ternal defects and to a. surface defect. While if pen P gives anindiin passing alternati cation such indication must bedue to aninternal the conductor, detecti defect. Thus We have provided a. methodand magnetic fields created by each t comprising me direct currentthrough the Here, too, if direct current is employed in magcurrentthrough the conductor under test, means net the flux passes into themagnetizable obresponsive to variations in the electromagnetic be pickedup as well as internal def t whil indicator actuated by said last-namedvariations.

to coil 30 but adapted to be energized by alter- P under test, means Win con earned thereby The output from up by said alternating current,and an indicator coils 32, may be caused to operate pens P and incomparative relation to said first indicator and P in the same manner asthe output from coils actuated sald lastnamed vanatlpns' 12,13 and 7. Adevice for detectmg flaws in electrical In accordance with theprovisions of the conductors and for diiferentiating between in entstatutes, we have herein described the printernal defects. and otherdefects compnsmg 2 desire to have it understood that the apparatuscurrent an mdlcator actuated by sald va- 1 5 1 scribed, some of thesemay be altered and others actuated Py sald last named Vanatlons said cont th 't eral results outlined, and the invention extends g g i g gi gggz gfii32 2 23 22231 to suck} objects, and for differentiating betweeninternal Having dBSCIIbEd our invention, what we claim defe ts and otherdefe t comprising a magnetic and desire to secure by Letters Patent is:

including a portion of said object, means for D. C. flux, meansresponsive to variations in flux through said objects, means forindicating said variations, a second magnetic circuit including aportion of said object, means for energizing said second circuit with A.C. flux, means responsive to variations in said last-named flux throughsaid object, and means in cooperative relation to said first indicatingmeans for indicating said lastnamed variations.

HARCOURT C. DRAKE. LOREN J. DE

